The invention relates to an antenna device. The antenna device particularly serves for transmitting and/or receiving electromagnetic signals.
At present, radar-based driver assistance systems, radar-based sensors like filling level or distance and velocity measuring means, but also communication systems for high-bit-rate wireless data transmission, systems of security technology, building surveillance and indoor navigation advantageously operate in the high GHz frequency range. All the applications mentioned use antennas having a certain directional effect or directivity which usually additionally has to be variable in space. With radar systems as are, for example, used in “adaptive cruise control” systems in automobile industry, the directivity serves for spatially detecting the target. With high-bit-rate communication systems, reusing the frequency spectrum is made possible by directive emission. In addition, transmission losses between transmitter and receiver are compensated partly by means of using antennas of directive emission, and spurious reflections can be masked out.
Spatially steering or turning the beam direction of an antenna can be performed mechanically using actuators as is, for example, the case with parabolic antennas for radio astronomy. This way of adjustment is very precise, but the times for obtaining a certain position are in the range of minutes. Very fast steering in the range of microseconds, in contrast, is made possible by so-called phased array antenna systems which consist of a plurality of individual antennas (frequently of a planar setup) and which each comprise an electronically adjustable phase shifter. For achieving directivity, phased array antennas use at least two individual emitters. Additionally, a complicated drive network is used.
Frequently, combinations of slower, mechanic and faster, electronic beam steering are used.
Microwave antennas are frequently realized as separate components on substrates suitable for microwaves like, for example, aluminum oxide ceramics, Al2O3, and connected to the active component (transmitter, receiver) via a conducting connection. Wafer-level integration of on-chip antennas on silicon has been examined intensely for many years. The desire for miniaturization and cost reduction plays an important role here. In [1], inverted-F and Yagi antennas on a silicon substrate are described and first measuring results presented. The steerability of the directional pattern, however, is not examined here.
A 77 GHz transceiver integrated on silicon-germanium SiGe having a phased array arrangement consisting of four emitter elements for beam steering is described in [2]. Thus, every emitter element is driven by means of a circuit including two mixers, a phase shifter and a power combiner. Increasing the microwave power emitted entails one power amplifier each for every antenna element. The integrated antenna elements are simple dipole antennas. However, the overall circuit complexity is immense.
An antenna arrangement for a frequency of 60 GHz including five monopole antennas which are driven by digital phase shifters switched by means of MEMS switches is described in [3]. The phase shifters are switchable in steps of 20 degrees and thus only allow discrete beam steering.
A first suggestion for a mechanically steerable antenna pattern using MEMS can be found in [4]. It deals with a half-wave dipole, the arms of which can be moved independently of each other using MEMS linear actuators.
[5] describes an arrangement suggesting electronic and MEMS-based mechanical steering of the directional pattern of the antenna. Here, every antenna element of an array arrangement is implemented to be steerable individually. Additionally, varying the drive phase is suggested. This arrangement is based on an optical 2D scanner having mirror areas of 400 μm×400 μm [6]. Patch antennas for a frequency of 76.5 GHz, however, entail an area of at least 800 μm×600 μm. Additionally, it is not described how the individual antenna elements are to be driven.
A mechanically steerable 2×2 patch array for a frequency of 60 GHz is described in [7, 8, 9]. The structure is formed on a glass substrate, a dielectric polymer material benzo-cyclo-butene (BCB) is used for suspension and a substrate material for the antennas; the structure is stabilized by means of a silicon frame. Steering takes place using magnetic forces around two axes by an angle of +−20 degrees. However, the structure is complex and an additional integration of active components seems to be doubtful.
It is the object of the invention to present an antenna device which allows miniaturization without having to deal with significant losses in the radiation characteristics.